[They did say they would share. Oikawa's just entirely convinced Yamaguchi doesn't want to any more, so his milkshake will sit there, closer to Yamaguchi than Oikawa while Oikawa is entirely fascinated by his bread. Which is excellent and delicious and he likes a lot and is absolutely a better thing to be looking at than the cute boy sitting opposite him who is probably one step away from going home.]
nooo, don't be. she makes me cry every time we exchange headcanons, this is good payback